Decreased ulnar bending stiffness in osteoporotic Caucasian women.

Mechanical response tissue analysis (MRTA) is a noninvasive measure of ulnar bending stiffness in vivo. It is unique in that the mechanical response to the lower range of vibrational frequencies is used to determine the average cross-sectional bending stiffness. The objective of this study was to compare ulnar bending stiffness among normal, osteopenic, and osteoporotic Caucasian women. World Health Organization criteria were used to define cohorts. Ulnar bending stiffness was expressed as the product of Young's modulus of elasticity (E) and the cross-sectional moment of inertia (I) in units of square Newton meters using MRTA. There was no difference in the mean body weight between cohorts but mean age was significantly different (p < 0.0001, analysis of variance): normal women, 34 +/- 12 yr (n = 55); women with age-related/idiopathic osteopenia, 52 +/- l l yr (n = 36(; and women with osteoporosis, 65 +/- 10 yr (n = 24). The mean EI of osteoporotic Caucasian women (25 Nm(2)) was 25% lower than normal subjects (33.1 Nm(2)) (p < 0.0001). However, there was no significant difference between EI of normal women and osteopenic women (30.l Nm(2)). EI was significantly but weakly correlated (i.e., the greatest r(2) value was 37%) to all dual X-ray absorptiometry variables, ulnar width, age, and body weight. In summary, results with MRTA were consistent with previous studies using classical ex vivo biomechanical techniques and in vivo vibrational techniques, showing decreased strength (i.e., bending stiffness) in osteoporotic bone compared with normal bone and a generalized decrease in bending stiffness with increasing age.